The new amount of storage space will give people who use Google services the most generous storage capacity of any player in the free online-storage game. A quick look at competitors shows that Dropbox currently starts free subscribers at 2GB, Microsoft SkyDrive users get 7GB, and Apple iCloud, Amazon Cloud Storage, and SugarSync offer 5GB for free. The announcement follows a Google Drive update from last week that allows you to save files from the Web directly to Drive.

There's no doubt that the 15GB is a game-changer in the free storage market. The question is, why did Google do it?

Nevermind "do no evil," Google -- as we all know -- is in the business of making money. If Google is offering you more storage, then there is something that extra storage helps you do that will help Google make more money.

What that is, Google is not saying -- yet.

It's possible that at I/O, Google will reveal that Drive or Google+ will incorporate a more multimedia approach. Or perhaps it's simply nothing more than a shot across the bow of Dropbox: you now get 15GB because Google can give you 15GB.

Either way, it makes Gmail, Google+, and Google Drive that much more appealing to serious Google services users.

Update, 7:03 p.m. PT: Added that business using Google Apps will see their storage increase to 30GB.

Update, 10:47 a.m. PT: Clarified that the new storage capacity is shared by Gmail, Google+, and Google Drive.